Lithium versus Lead Acid batteries

We chose to use a lithium battery in the van. It was the right choice for us and our power and space requirements. Other people choose lead-acid batteries either for the lower cost or just because they are more traditional. Here’s how to work out which is right for you…   

There are two main types of battery you can use for storing power in your van; lithium and lead-acid. Within each of those types there are different styles. Each is suited to different purposes.

Lead-acid battery types

The most normal “car battery” type of lead-acid battery is the wet cell battery. This has little caps on the top that unscrew so that you can add more liquid to the battery as it gets evaporated off. The “liquid” is sulphuric acid (that’s the “acid” part of the lead-acid name). It needs to be checked regularly to make sure the acid is completely covering the lead plates in the battery.

Because they give off hydrogen and oxygen gas when they’re charged and discharged, these batteries aren’t designed to be placed in the living area of the van. They can also leak sulphuric acid, or expel it as a gas, so things in the immediate vicinity of the battery can get corroded or rusted. If people use them for Sprinter conversions, they will often make a battery holder to put this style of battery under the van – often in the place where the spare wheel normally sits.

For conversions, most people tend to use Absorbed Glass Mat (AGM) or Gel batteries because these don’t need the same level of attention as regular wet cells. The acid in these batteries is held in place by a fiberglass mesh (AGM) or a gel substance. That means the battery doesn’t have caps on the top to add more acid. Most can even be used on their side with the terminals on one edge. That often makes it easier to find a place to put them in the vehicle. It’s also marginally safer to use these batteries inside the vehicle. They can still give off hydrogen, but normally only when something is going very wrong with the battery.

Most car batteries are 12 volt units, but you can also buy 6 volt batteries meant for golf carts. These tend to be more durable and long-lasting because they’re designed for tougher treatment – deeper charge/discharge cycles. Hooking two 6v batteries together in series gives you 12v. Put together this way they can be charged with a regular 12v charger.

I’m not going to list vendors here. You can pick these batteries up at most automotive stores. You might have to do some research into the relative merits of different battery manufacturers and models. With lead-acid, higher prices are normally an indication of higher quality. It means the batteries are made with thicker lead plates inside them and better attention to engineering tolerances.

Some concerns with lead-acid batteries

Lead-acid batteries tend to dislike being regularly discharged beyond 50%. That means the usable amp-hours of your battery system are about half of the stated amp-hour rating.

It gets worse, though. There’s a thing called the Peukert effect. In practical terms, during discharging, if you pull a high current from the battery it “uses up” some of your amp-hour capacity. In other words, a 200 amp-hour battery (that’s 100 amp-hours of usable capacity) being discharged at a 100 amp rate will not last for an hour, like you’d expect. It will last for a much shorter period of time (somewhere around 33 minutes to 50% discharge).

Also, depleting the battery that quickly will lead to pretty major sulphation. That’s a build-up of sulphur being deposited from the sulphuric acid on to the lead plates. It makes the lead plates less efficient at storing electricity and it’s hard to reverse.

Over-stressing the battery also makes it heat up. Heating it too far can make the electrolyte boil off. Even sealed batteries like absorbed glass mat versions will still boil off in an emergency.

Lithium battery types

The Boeing Dreamliner batteries that made the headlines in 2012 for catching on fire while in service were LiCoO2 (Lithium Cobalt Oxide) based. This is the same technology used in many of the cheap hoverboards that have been recalled in the USA and Australia. The Cobalt Oxide batteries can suffer from thermal runaway if they are overcharged, overheated, short circuited, or damaged.

Luckily, most of the lithium batteries used in van conversions are Lithium Iron Phosphate (LiFePO4) based. Some may also be Manganese Oxide (LiMn2O4) or Manganese Iron Phosphate (LiFeMnPO4) based. These types have a slightly lower energy density, but they keep their charge very well in storage, have a higher number of charge cycles, and have better safety.

You can read more about lithium battery safety, but let’s just say you aren’t going to be carrying a highly explosive chunk of metal around with you if you use LiFePO4.

Using lithium batteries in a conversion

Many of the RV guides to 12 volt systems were written before lithium batteries were available at a suitable price point. There’s not a lot of information out there, and there is some misinformation and hearsay.

Charging differences

The biggest difference between lithium and lead is the charging profile they want. Lead batteries will “bulk” charge quite quickly to around 80%, then they need a long time in “absorb” mode to fill up the remaining 20%. After that, they need to be “floated” to keep them near 100% charge. Leaving them only partially charged for a while can hurt them.

Lithium batteries will typically take as much bulk charging power as you can give them all the way up to 100%, so they don’t need a long time in “absorb” mode. They also don’t need to be kept topped off. They don’t care what state of charge they are in. The charging voltage for lithium is also different to that of lead.

In other words, if you try to use a battery charger meant for lead acid batteries to charge your lithium battery, it won’t be very effective. Luckily there are lots of good quality inverters, chargers, and battery combiners that let you set a specific charge profile. We used equipment made by Victron Energy. It’s highly programmable for different charge profiles.

Faster charging from solar

Because of the difference in charge profile, lithium batteries charge much faster either from a solar system or a generator. They will take all the power that the charging system can feed them, without having to tail off into an “absorb” mode.

Temperature considerations

Most lithium batteries don’t like being charged up in sub-zero temperatures. You’ll probably want to place the battery inside the living area of the van, or in a well-insulated box under the van with a 12v heating pad.

Higher cost

The up-front cost of lithium is about 2x to 4x the equivalent cost of a lead-acid system of the same usable capacity. However, the service life of lithium battery packs is at least 10 years if they are well treated, compared to 3-5 years for most lead-acid batteries. Overall lithium tends to come out ahead in lifetime amp-hour comparisons. It’s just a question of whether you have the available funds right now.

Smaller size and lower weight

Here’s where lithium batteries come in to their own. They are 3 – 4 times smaller than the equivalent lead-acid battery for a given amp-hour rating. Because you can discharge them further (about 70-80% rather than 50%) you can use a smaller capacity battery. They also weigh much less. Neither of these concerns would matter very much if you were just adding battery backups to a house. It makes a world of difference if you’re doing a van conversion. Using lithium batteries means you’ll free up more of your payload for other items, and take up less storage space at the same time.

Buying lithium batteries

Several manufacturers make LiFePO4 or similar batteries, in multiple formats. The raw cells produce 3.6v so you need four of them to make the equivalent of a 12v battery. You also need a battery management system that will prevent the battery from getting hurt by under- or over-charging. Lithium batteries also need a different charge profile to lead-acid batteries.

Because it’s a newer technology, you might have to do a bit more research in order to put together a good system. This makes the whole thing sound scary, but there are plenty of people out there who’ve done this themselves already.

Vendors who can help specify a system

Doing a DIY battery install might seem daunting, but it’s a lot cheaper than the pre-built options and you get more control over the system you end up with.

There are a couple of well-respected vendors in the electric vehicle space who are happy to spend the time getting you up and running. Buying from them means you have access to (some) support from people who know what they are talking about.

Most van installs will want between 200 and 500 Amp-hours of lithium battery capacity. You can work out your battery capacity needs here.

    • The Electric Car Parts Company in Salt Lake City, UT has been helpful to several Sprinter Forum members.
    • Manzanita Micro is a WA company with some experience in battery packs for van conversions.
    • Thunderstruck sells CALB battery cells. As a comparison to the pre-built options, four of their 100Ah cells and a (real) BMS would cost $625.
    • Elite Power Solutions sell batteries and BMS systems. They are somewhere between do-it-yourself and pre-built, in that they can provide all the pieces you need but it’s not exactly a drop-in replacement battery.

  • AM Solar has started selling kits using Victron equipment. If you don’t want to do the research yourself, their kits (and advice) look pretty good. For $2800 you can get a full 200Ah battery bank with battery management system (that will hook in to your alternator for charging) and all the pieces you need to put it together. For $5000 you get a 400Ah version.

Buying a pre-built unit

If you really don’t want to take the time to learn how to bolt connectors on to some raw cells and wire up a battery management system, there are plenty of companies who will take your money and give you a pre-built battery that is a drop-in replacement for a lead-acid version. My concern with these systems is that you have no insight into how the battery management system actually works. After reading some posts on the Sprinter forum, it seems that some of the manufacturers (or U.S. resellers) of these boxes also have no insight into how they work.

These things can be costly compared to the DIY options. In fact, I think they are primarily what gives lithium batteries a bad name for being expensive. You are paying for convenience, but in most instances you are also giving up control because it’s hard to manage the batteries when they are sealed away in a box. It’s also not clear which manufacturer’s cells are inside each box. Not all lithium cells are created equal.

Here are some of the vendors in this space.

  • Victron make pre-packaged Lithium batteries with or without a built in BMS connection cable that work very well with the rest of their electrical components. $950 per 90Ah battery. They also sell 200Ah batteries.
  • SmartBattery make SB100 drop-in lithium replacements in sizes that correspond with regular lead-acid batteries. Their Group 27 80Ah battery is $1050. One forum member installed these in his RV and had trouble getting straight answers from the company. It’s not clear they really know what they are selling. Also, they have a battery *protection* system built in, not a battery *monitor* system. In other words, the battery will shut itself down if it’s seriously over- or under-charged, but won’t actively manage the cells inside the battery.
  • Stark Power make 125Ah drop-in replacement batteries for $1440. Again, they claim to have a built-in BMS which they claim does cell balancing as well as providing an under/overcharge cutoff.
  • Lithionics have batteries corresponding to most common dimensions, and build some pretty large capacity packs too. They offer an 8D sized 400Ah battery with a built in BMS, for instance. Their BMS has a wireless access module. The BMS offers over/undercharge, balancing, and short circuit protection.
  • NexGen batteries have built in balancing and under/overcharge protection. Their 300Ah battery is $3500. Their 100Ah battery is $1300. They offer free shipping on their site.
  • Relion make 100Ah drop-in batteries for ~ $1300. and 300Ah batteries for ~$3500. According to the specs, the larger batteries have an RS232 port for monitoring. However, the chargers sold on the site don’t make use of this port, and there doesn’t appear to be a BMS available on the site. The Relion site also looks very SEO-optimized (lots of republished articles, navigation menus that duplicate each other, etc.) which is never a good sign for a serious company.
  • LiFeBlue make several different sized drop-in replacement batteries. Their 300Ah model is 8D size and costs $2500. Their special “thing” is that you can get battery status information on your smart phone using bluetooth. It appears that their BMS does cell-level monitoring. One issue with this brand is that they’ve set the overcurrent threshold to 100A for 30 seconds. If you were using this battery to power a microwave or induction cooktop, you might exceed that discharge rate.
  • BioEnno make several sizes of LiFePO4 battery, with their 100Ah model costing around $900. It includes a BMS that balances.
  • Starlight Solar sell Lithium Iron Manganese Phosphate (LiFeMnPo4) batteries with a built-in BMS (with a horrible 1980s character-based video monitor). 100Ah for $1300, 500Ah for $4200. The systems are install-it-yourself, but the company claims to have experience with RV-based systems.
  • EVTV sell a 5200Wh (400Ah) battery for $4k. It’s got lots of fancy terms (“MILSPEC” just means it’s built to the specification that the military uses) and it’s hard to know how good the BMS is, but the company does at least have demonstrated experience with lithium battery technology. The provisos they mention apply to pretty much any lithium battery pack.
  • We bought from Balqon. We actually bought their pre-assembled system but it’s very bare-bones and it would have been incredibly easy to make it up ourselves just using their cells and the same BMS bought from a third party. They charge $2950 for a 400Ah system and $4480 for a 750Ah system. These prices are much better per Amp hour than some of the other pre-built options, but I wouldn’t use Balqon because of their poor customer service. Update: As of February 2017, Balqon’s site is down and their Facebook page lists them as “permanently closed.” Their batteries are Winston brand, so you could build your own system with these still if you can find a US vendor.

There are also some all-in-one lithium systems out there. We wouldn’t recommend them – they aren’t typically a good value for money, and they tend to have tiny batteries (100Ah or less). However, if you really, really can’t handle wiring and you want something that will charge your 12v electronics, run your 120v stuff (briefly), and recharge from solar or your house, then look at these options:

  • Goal Zero are selling their “solar generator” in a 1kWh (about 90Ah) Lithium version for $1000 exclusively through Costco. It’s called the Yeti 1000 Lithium and weighs 42lbs. 1500W pure sine wave inverter. That’s not a terrible price compared to the drop-in batteries, but you are still paying a lot for a small quantity of power. These are not LiFePO4 batteries. They are lithium nickel manganese cobalt oxide. That’s not an inherently good or bad thing. The NMC chemistry is also a relatively safe one.
  • The Enerplex Ascent is basically an orange version of the Goal Zero and is available at a very similar price.
  • Bannock make a similar 1.1 kWh lithium-based system called Ilios for around $1800. There are several more of these products out there – for instance , Inergy Kodiak , Solarpod, Humless, and one by Forty2Max with built in solar panels!  None of these are necessarily any better or worse than the Goal Zero, although they don’t have the sexy design touches and they might not have the same manufacturer support or easy return ability if you decide it’s not such a good idea.

Playing the long game

You can probably tell we’re fans of lithium battery technology. If you can afford it, lithium batteries are likely to work out cheaper over their lifetime than lead acid batteries, given the way that most people treat the batteries in their vans.

There’s currently a lot of talk about the price of lithium cells dropping steeply over the next couple of years as more of them become available and the manufacturing technology matures. There’s been a marginal price drop just in the year since we bought our system. There are some people who think it’s best to wait until the prices come down. They buy lead-acid battery systems now, with the intention of replacing them with a lithium setup in 3 to 5 years time when their current batteries die. That might be a good option, but on the other hand it requires an outlay now for devices (charger, etc.) that may not play nicely with a lithium setup. It might also involve buying a generator to keep the lead-acid batteries charged, which you could do without if you bought lithium batteries instead because you can fit more amp-hours into the van. When we bought our system, our thought was that even if we were paying a slight price premium, we would get all the benefits of lithium from day one and not have the hassle of re-building the system a couple of years down the line.

Having said that, there’s nothing wrong with a lead-acid battery system if you’re prepared to give it the oversight and maintenance that it needs, and if you have the storage space and available payload to carry the extra volume and weight of batteries.

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